C64 sound problems

I just inherited a Commodore 64, 1541 disk drive, some joysticks and various other related stuff. I've tried the C64 and 1541 by attempting to boot a couple of games that came with the package and it seems that the computer and drive work okay. The games come up and display their start screen. My problem is that the sound doesn't seem to work. The games came up silent when I suspect that they have some sort of music associated with their start screens and a simple Basic program that I typed in to test the sound also fails to produce any output. I know that the SID chips in these machines are prone to failure but I was wondering if there were any other likely causes of a lack of sound. The main reason I was interested in this machine was to play around with the SID so it will be very disappointing to find that it is bad. Is there anything other than a dead SID that can cause sound problems on a C64? Thanks David